I have a static IP, and /etc/network/interfaces is configured with a 'gateway x.x.x.1' entry.

Periodically, my server loses all internet connectivity, and when I can get to it for access, the default gateway is missing from the routing table.

Because this error halts all traffic to my server, I've set up a cronjob to periodically attempt to 'route add default gw x.x.x.1' so that I don't have to keep physically returning to the machine. I'd like a better solution...

Why doesn't the entry: up route add default gw x.x.x.1 work in /etc/network/interfaces to keep the gateway in the routing table? Moreover, shouldn't the 'gateway x.x.x.1' entry already make sure that the default gateway stays in the routing table?

Also, what log files should I be looking at in order to track down this reoccurring error?

Is there any way to make the kernel aware of the necessary gateway setting? I figured that /etc/network/interfaces would do that... Also, I am unsure of what is causing the problem, I just need a way so that when eth0 comes back up, the gateway route comes with it.
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Andrew ParkerMar 2 '12 at 3:28

I just wrote the answer: you should use your distro specific command. Period. This is also "ifip" and "ifdown" for RedHat.
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Gregory MOUSSATMar 2 '12 at 7:19

I am not sure about debian but redhat requires the sysconfig scripts to be configured in order to keep the gateway settings. I am not sure how relevant this is to debian but it drove me nuts on redhat.

All you need to do is add a one line GATEWAY=X.X.X.X to /etc/sysconfig/network. There's no way for the OS to automatically know what the gateway is, since it varies depending on the network.
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devicenullMar 2 '12 at 3:42

That is correct. I am not sure if debian uses the network sysconfig. Seems like it didn't last time I played with it.
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DaffyDucMar 2 '12 at 4:34

Okay, first off, why are you using ifconfig? On a normal server, you wouldn't touch that unless you were changing IP addresses.

I suspect you have a copy of the DHCP client running somewhere. I've seen intermittent issues like this when dhclient wakes up near the end of the lease expiration time. Make sure this is fully disabled (you can probably go so far as chmod -x or even removing it, as it has no real purpose on production servers). Check ps aux and make sure you don't see anything relating to DHCP.

Last, a DoS attack will not have any effect on your system's gateway address. It's possible it could cause the gateway to go down (if it overwhelms the router), but it would not cause your system to suddenly remove it from your routing table.

I'm just trying to trace what's happening to my server and why it keeps losing its route to the gateway (it just so happens that ifconfig up/down also does exactly this and I'm looking for a way to ensure that the gateway route comes up along with eth0). My server periodically goes offline, and I have to physically visit it to get it reconnected, and when I do, the route to the gateway is missing from the routing table... There's no DHCP, everything is static, no dhcp related items in ps aux.
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Andrew ParkerMar 2 '12 at 4:53

@AndrewParker It is probably not necessary to mention, but be sure to check for "dhclient" in the ps aux output, not simply for a pattern containing "dhcp".
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daffAug 14 '12 at 20:25